1. Field of the Invention
The present invention relates to a manual chain block, and more specifically to a manual chain block having a load sheave supported rotatably between a pair of side plates to be driven interlockingly by a manual actuating mechanism having a hand wheel.
2. Description of Prior Art
Conventionally, for example as disclosed in the Japanese Utility Model Publication No. Sho. 62 (1987)-16477 and as shown in FIG. 22, a manual chain block has a load sheave 103 supported rotatably between a pair of side frames 101, 102. A driving shaft 104 is inserted into a shaft bore of the load sheave 103, and a hand wheel 105 which is part of an actuating mechanism is threadably engaged with axial one end of the driving shaft 104. The inside of the hand wheel 105 is connected to a driven hub 106 with a reverse prevention gear 107 and a pair of lining plates 108, 109 interposed between a flange portion of the driven hub 106 and the hand wheel 105 as well as a reverse prevention pawl 110 is pivotally mounted to the side frame 101 so as to engage with the reverse prevention 107, thus providing a transmission mechanism 111 with a mechanical brake. A reduction gear mechanism 112 is mounted to the axial other end of the driving shaft 104.
In addition to the above-mentioned construction, a wheel cover 113 for covering the transmission mechanism 111 and the hand wheel 105 is attached to the side frame 101, and a gear cover 114 for covering the reduction gear mechanism 112 is attached to the side frame 102. These covers 113, 114 are joined integrally to the side frames 101, 102 respectively by a stay bolt 115. A hook 116 is attached to upper portions of the side frames 101, 102 through an attachment shaft 117, and a chain kicker 118 is attached to lower portions thereof.
The driving shaft 104 arranged as mentioned above is supported rotatably at one axial end portion extending outward beyond the side frame 102 by a radial bearing 119 mounted to the gear cover 113 with its other axial end portion which extends outward beyond the side frame 101 being in the free state and threadably engaged with the hand wheel 105 and its intermediate portion being supported rotatably by a radial bearing 121 within a shaft bore of the load sheave 103. The transmission mechanism 111 and the hand wheel 105 are assembled onto the free end portion of the driving shaft 104 outside its supported portion.
Incidentally, numeral 122 in FIG. 22 designates a stopper for restraining axial movement of the hand wheel. Accordingly, the hand wheel 105 is threadably advanced by operating an endless hand chain (not illustrated) looped around the hand wheel 105 to further transmit to the driving shaft 104 a driving force transmitted from the hand chain to the hand wheel 105 through the transmission mechanism 111 and then transmit the driving force to the load sheave 103 through the reduction gear mechanism 112 so that cargo lifting can be carried out by winding up the load chain (not illustrated), a lifted cargo position can be held by the mechanical brake and a cargo lowering can be carried out by reversely operating the hand chain through the mechanical brake.
In the above-mentioned conventional construction, however, since the intermediate portion of the driving shaft 104 is supported by the load sheave 103 through the bearing 121, it is necessary to fit the bearing 121 into a small limited annular gap defined between an inner peripheral surface of the shaft bore of the load sheave 103 and an outer peripheral surface of the driving shaft 104. Therefore, since the size and type of the bearing 121 are so restricted that only a bearing having a poor bearing efficiency such as a needle bearing and a sleeve bearing can be employed, there is a problem that transmission efficiency of the driving force to the load sheave 103 becomes so poor that a larger operation force is needed for operation of the hand chain. Further, since the portion of the driving shaft 104 on the side of the actuating mechanism is not supported like a cantilever and provided at its free end with the hand wheel 105, the driving shaft 104 is deflected by a load acting on the hand wheel 105 when the wheel 105 is driven by the hand chain. Thereupon, when the hand chain is operated forcibly under that deflected condition of the driving shaft 104, there is also a problem that a bending stress is concentrated on the driving shaft 104 outside the load sheave 103 and its journal portion is deformed.
When the driving shaft 104 is deflected or deformed in that way, the hand wheel 105 is brought into contact with an inner surface of the wheel cover 113 or a component member such as a chain guide which is provided in the inner surface of the wheel cover 113. As a result, the transmission efficiency becomes much worse and an unpleasant noise is generated.